In the design of semiconductor devices, analysis of these devices is often desired under certain test conditions. Such analysis is particularly beneficial with respect to integrated circuits (IC) for isolating points of potential failure. It is well known that in IC operation, fault conditions or failures can cause extremely faint photon emissions. These photon emissions can be detected by an emission microscope such as the one described in U.S. Pat. No. 4,680,635 to Khurana.
Khurana describes an invention wherein an IC is placed on a microscope stage with the area to be inspected centered in the axis of the optic system and camera. A light tight chamber is closed around the microscope, the IC is illuminated, and while being viewed through the CRT display by the operator, positioned with the area of interest in the microscope axis. An image is then obtained through the video camera of a reflected light top view of the structural pattern of the IC. The image is digitized and stored in memory. The illumination source is then turned off and without applying any power, background noise light from the inspection area is collected. This background image is then digitized and stored in memory. A failure condition "test vector" of voltages is applied by manual switches to the I/O terminals of the IC causing leakage current conducted through defective dielectric features to emit extremely faint visible and infrared light. This emitted light is collected and amplified to obtain an emitted light image which is digitized and stored.
A user can thereafter subtract the background image from the emitted light image to cancel out any background noise. A further filtering process is performed to separate emitted light points from the random noise bright points. A failure engineer can then take this final image and superimpose it over the original illuminated composite image to locate the exact location of any possible faults.
U.S. Pat. No. 4,755,874 to Esrig et al. also describes an emission microscope similar to Khurana. The benefit here, however, is the addition of a magnification lens providing for a larger viewing area. This allows a user to view the entire IC at one time and identify dynamic failure condition defects.
A drawback with the above two referenced patents is that they both require a darkbox to shield the IC under test from external light. Darkboxes tend to be large and bulky and by their very nature, are not portable. What is therefore needed is an emission microscope workstation that is portable. What is further needed is a system wherein the camera can be interfaced with existing microscope optics associated with production testers for on-site emission acquisition. This improves portability and decreases costs. What is still further needed is a system that provides for true color emission acquisition imaging which allows multiple emission sites on a die to be spatially resolved and categorized with qualitative spectral emission software.